1. Field of the Invention
The present invention relates to a mobile communication system and a method of controlling operation thereof, and particularly, to an improvement of a RNC (Radio Network Controller) in a W-CDMA cellular mobile communication system.
2. Description of the Prior Art
An architecture of a W-CDMA communication system that is a mobile communication system is shown in FIG. 23. A radio access network (RAN) 1 is configured with radio network controllers (RNC) 4, 5 and Node B6 to 9, and is connected with a core network (CN) 3 as an switching network via an Iu interface. The Node B6 to 9 are logical nodes for radio transmission/reception, and more specifically radio base station apparatus.
An interface between the Node B and RNC is referred to as Iub, and Iur interface is also standardized as an interface between RNCs. Each Node B covers one or more cells 10 and is connected to a mobile unit (UE) 2 via a radio interface. The RNC manages the Node B and selectively combining and splitting radio paths . Note here that the detail of the architecture shown in FIG. 23 is specified in 3GPP (3rd Generation Partnership Projects).
FIG. 24 shows protocol architecture of the radio interface in the W-CDMA communication system shown in FIG. 23. As shown in FIG. 24, the protocol architecture is composed of three protocol layers of a physical layer (PHY) 11 denoted as L1, a data link layer 12 denoted as L2, and a network layer (RRC: Radio Resource Control) 13 positioned in an upper layer of the data link layer 12 and denoted as L3. The data link layer L2 includes two sublayers of a MAC (Media Access Control) layer 121 and a RLC (Radio Link Control) layer 122.
An ellipse shown in FIG. 24 indicates a service access point (SAP) between layers or sublayers, where the SAP between the RLC sublayer 122 and the MAC sublayer 121 provides a logical channel. That is, the logical channel is provided from the MAC sublayer 121 to the RLC sublayer 122, and is classified by functions and logical properties of a signal and characterized by contents of transferred information. The logical channel includes, for example, common channels of CCCH (Common Control Channel) and PCCH (Paging Control Channel), dedicated channels of DCCH (Dedicated Control Channel) and DTCH (Dedicated Traffic Channel), or the like.
The SAP between the MAC sublayer 121 and the physical layer 11 provides a transport channel which is supplied from the physical layer 11 to the MAC sublayer 121. The transport channel is classified by a transmission form and is characterized depending on how and what information is transmitted via a radio interface. The transport channel includes, for example, a FACH (Forward Access Channel), a RACH (Random Access Channel), a PCH (Paging Channel), a DCH (Dedicated Channel), or the like.
The physical layer 11 and the data link layer 12 are controlled by the network layer (RRC) 13 via a C-SAP providing a control channel. The detail of the protocol architecture shown in FIG. 24 is specified in ARIB STD-T36-25.301v.3.8.
In the conventional art, there exists a C (Control) plane that controls signaling, and a U (User) plane that transports user data.
The RNCs 4, 5 of the radio access network (RAN) 1 in the conventional art are apparatuses in which both functions of the C plane and U plane are physically integrated. By such a single apparatus in which both the functions are integrated, a radio bearer service is provided to a mobile unit.
In a mobile communication system including such a conventional RNC that integrally has the functions of both U plane and C plane, if we need to enhance the function of C plane, however the RNC itself should be added in the system. In the same way if we need to enhance the function of U plane, however the RNC itself should be added in the system. Therefore, the conventional RNC constitution makes constructing a system with high scalability quite difficult.
In the radio access network, it is conceivable to separate the C plane and the U plane from a conventional RNC, however, for realization of such separation, a device responsible for the C plane is required to utilize a bearer service provided by a device responsible for the U plane to receive or transmit signal to the mobile unit. Therefore, it is necessary to set a logical connection between the device responsible for the C plane and the device responsible for the U plane in order to transmit/receive signal.
At this time, there exists disadvantages that the device responsible for the U plane must identify a plurality of logical connections, to provide appropriate bearer services, and also that the devices responsible for the C plane must identify the logical connection to receive signal from the mobile unit or transmit signal to the mobile unit.